1. Field of the Invention
The invention relates to articles comprising magnetostrictive alloys, in particular, cobalt-iron-based magnetostrictive alloys.
2. Discussion of the Related Art
One application for highly magnetostrictive materials is magnetostrictive transducers, which convert electrical energy into mechanical energy or vice versa. Such transducers are useful for ultrasonic sound generators, magnetostrictive tuning in optical systems, acoustic delay lines, and other actuators and sensors. See, e.g., F. Claeyssen et al., J. of Alloys and Compound, Vol. 258, 61 (1997).
Important requirements for practical application of magnetostrictive materials include the capability to provide high saturation magnetostriction in low applied fields, ease of fabrication into a desired shape, e.g., ductility and formability of the material, and low cost. The magnetostriction of Co--Fe alloys has been studied in previous work (see, e.g., R. C. Hall, Trans. Metall. Soc. AIME, Vol. 218, 268 (1960)). For example, a saturation magnetostriction of 130.times.10.sup.-6 under a field of .about.2000 Oe has been obtained on a cold rolled Co-30%Fe tape after 95% deformation (see E. A. Nesbitt, J. Appl. Phys., Vol. 21, 879 (1950)).
High saturation magnetostriction values in excess of 1000.times.10.sup.-6 have been reported for TbFe.sub.2 and other iron rare-earth compounds known as giant magnetostriction materials or terfenol. See, e.g., A. E. Clark, Ferromagnetic Materials I, edited by E. P. Wohlfarth, North Holland, Amsterdam, Chapter 7, 531 (1980), and R. E. Newnham, MRS Bulletin, 20 (May 1997). These materials, however, are brittle and require the use of a high magnetic field, typically 1000 Oe or higher, to obtain high magnetostriction. More recently, large magnetic-field-induced strains have been observed in magnetic shape memory alloys such as Ni.sub.2 MnGa. See, e.g., R. C. O'Handley, J. Appl. Phys., Vol. 83, 3263 (1998) and J. K. Ullakko et al., Appl. Phys. Lett., Vol. 69, 1966 (1996). These intermetallics, however, generally require single crystals or high magnetic fields to exhibit substantial magnetostriction.
Thus, improved magnetostrictive materials are desired, particular materials which not only exhibit good magnetostriction at relatively low applied field, but which are also capable of relatively easy formation, handling, and incorporation into devices.